The present invention relates to a system for controlling ignition timing in an internal combustion engine and a method therefor.
Conventional ignition timing control systems are exemplified by Japanese Patent Applications Unexamined Open No. Sho 54-142,425 (abbreviated as reference AA) published on Nov. 6, 1979, No. Sho 53-56,429 (abbreviated as reference AB) published on May 22, 1978, and No. Sho 58-82,074 (abbreviated as reference AC) published on May 17, 1983.
The reference AA discloses the same system, wherein the ignition timing is controlled so as to retard the ignition timing for avoiding the recurrence of knocking when a measured level (intensity) of knocking in the engine exceeds a predetermined threshold value.
The reference AB discloses the same system, wherein variation in pressure within a combustion chamber (referred to as cylinder pressure) of an engine cylinder is detected, and a corrective control of the ignition timing, i.e., so called Minimum Spark Advance for Best Torque is performed (hereinafter referred simply to as MBT control) in such a way that on the basis of a crackshaft rotational angle .theta..sub.pmax (hereinafter simply referred to as crank angle) at which the cylinder pressure has reached its maximum, the crank angle .theta..sub.pmax coincides with a predetermined target crank angle .theta..sub.M at which torque of the engine reaches its maximum.
The reference AC discloses the same system, wherein in addition to the MBT control, the ignition timing is so controlled as to retard the ignition timing for avoiding the recurrence of knocking taking a higher priority than the MBT control when the engine knocking is detected from a detection signal of strong fluctuations in combustion chamber pressure and a level (intensity) of detected knocking exceeds a predetermined value (until the level of knocking reduces and passes through the predetermined level).
The ignition timing control systems disclosed in the above-identified references have respective drawbacks described below.
In the conventional system disclosed in the reference AA, the control mode merely avoids recurrence of knocking whenever the knocking has occurred. In detail, since the corrective control of ignition timing is merely repeated for avoiding recurrence of knocking only after the knocking has actually occurred, such a control mode as to prevent the occurrence of knocking cannot be achieved before the knocking has occurred.
In the ignition timing control system disclosed in the reference AB, since the corrective control of the ignition timing is merely repeated in a proportional-integral (PI) control mode on the basis of a deviation between the crank angles .theta..sub.pmax and .theta..sub.M, the correction value of the ignition timing is largely changed when the engine operating state is changed so that a variation of engine output torque is brought about. This results in a reduction of the engine driveability-characteristics.
In the conventional system disclosed in the reference AC, such as a control as to prevent occurrence of knocking cannot be achieved since the corrective control of ignition timing is repeatedly carried out only after the occurrence of knocking and the engine output power is accordingly reduced.